*2.2.3 The "Sequence Theory"*

1.Howard and Fiske [18] more elaborated the above theories. The authors stated that biological control would be more efficient if only one developmental stage of the pest species is attacked. Biological control should be achieved through a variety of natural enemies attacking several developmental stages of the host, making a sequence of natural enemies for satisfactory control.

	- 1.Curtis P. Clausen (1951) highlighted the time factor theory for introduction of biological control agents. He stated that an effective natural enemy might be expected to show evidence of control at the point of release within a period of 3 host generations or 3 years and concluded the following:
		- a.A fully effective natural enemy is always easily and quickly established.
		- b.If failure occurs, it indicates that the control will not be fully effective even after establishment is achieved.
		- c.Further, the colonization of exotic species, to be used as biological control agent, may be discontinued after 3 years, if it fails to establish.
